Case Report Fetal Escape From the Amniotic Sac Follow-up From First Trimester to Delivery Zvi Leibovitz, MD, Shlomi Barak, MD, Simon Degani, MD, Israel Shapiro, MD, Gonen Ohel, MD Rupture of the amniotic membrane with its subsequent disintegration may cause the fetus to appear in the chorionic cavity. This has been described previously as occurring after amniocentesis and fetal surgical procedures 1 3 ; however, the spontaneous escape of the fetus through a defect in the amniotic membrane in the early second trimester is an extremely rare event. In this report, such an amniotic escape is presented with its sonographic follow-up and postpartum findings. The clinical importance of this peculiar disorder is discussed. Case Report Abbreviations CAS, chorion-amnion separation Received August 22, 2005, from the Department of Obstetrics and Gynecology, Bnai-Zion Medical Center, Haifa, Israel; and Faculty of Medicine, Technion, Haifa, Israel. Revision requested August 30, 2005. Revised manuscript accepted for publication September 7, 2005. We thank John Waldman, MD, for his contribution in preparing the manuscript. Address correspondence to Zvi Leibovitz, MD, Department of Obstetrics and Gynecology, Bnai- Zion Medical Center, PO Box 4940, Haifa 31048, Israel. E-mail: zvi.leibovitz@b-zion.org.il A 38-year-old woman, gravida 2, para 1, was referred to our prenatal ultrasound unit at 11 weeks gestation with lower abdominal pain. She had an unremarkable medical history. In her first pregnancy, she had cervical cerclage at 19 weeks gestation because of cervical shortening and cesarean delivery at term because of breech presentation. The 11th week transvaginal sonographic examination of her current pregnancy revealed an intrauterine sac appropriate for gestational age with a live embryo of 4.1 cm crown-rump length. Gestational sac dimensions were 6.6 5.8 2.9 cm; mean sac diameter was 5.1 cm. Both measures (crown-rump length and mean sac diameter) were in exact correlation with the gestational age; however, the scan showed a reduced volume of amniotic fluid, resulting in tight entrapment of the fetus by the amniotic membranes. Interestingly, the scan showed a normalsized chorionic space, as determined by mean sac diameter (Figures 1 and 2). 2005 by the American Institute of Ultrasound in Medicine J Ultrasound Med 2005; 24:1745 1751 0278-4297/05/$3.50
Fetal Escape From the Amniotic Sac Figure 1. Transvaginal sonogram at 11 weeks shows an appropriate-for-gestational-age crown-rump length (4.11 cm). In this longitudinal plane, the amnion is invisible because of the location of the amniotic membrane close to the fetus. Line b indicates the scanning plane in Figure 2; and asterisk, chorionic cavity. At 13 weeks gestation, a transvaginal sonographic examination showed a well-developed, appropriate-for-gestational-age fetus wrapped by loose amniotic membranes (Figures 3 5). The amniotic sac was smaller than expected, and the chorionic space was expanded. The gestational sac dimensions were 7.0 6.8 3.5 cm, resulting in a mean sac diameter of 5.8 cm, which is standard for the gestational age. A left clubfoot was suspected on this examination (Figure 6). At 15 weeks gestation, the transvaginal sonographic examination showed an appropriately growing fetus with near-normal amniotic fluid volume but prominent chorionic space surrounding the amniotic membrane (Figures 7 and 8). Except for the left clubfoot (Figure 9) and the Figure 2. Transvaginal sonogram at 11 weeks. The scanning plane crosses the fetal body along line b in Figure 1. In this axial plane, the amnion (arrows) appears close to the fetus. Notice the diminished amniotic fluid volume and relatively expanded chorionic cavity (asterisk). left ventricular echogenic focus, the anatomic scan showed no abnormalities. The placenta was located in the posterior uterine wall and had central insertion of the umbilical cord. This important fact is evident in the images of the 23rd week. We discussed with the patient the risk of chromosomal abnormalities in view of maternal age, left ventricular echogenic focus, clubfoot, and chorion-amnion separation (CAS). As a result of this discussion, genetic amniocentesis was performed at 16.5 weeks under sonographic guidance. The procedure was uneventful. By a single tap in the anterior uterine wall, approximately 30 ml of the clear amniotic fluid was obtained. Chromosomal analysis showed a normal 46,XY karyotype. The α-fetoprotein concentration was within normal limits. A sonographic examination 3 weeks later (19.5 weeks gestation) revealed new findings. The amniotic membranes did not appear to enclose the fetus and were shown near the fetus as irregularly folded echogenic sheets (Figures 10 13). The fetal movements freely displaced them. On prolonged inspection, the fetus showed normal body and limb movements without persistent attachment of any fetal part to the abnormal membranes. Fetal growth was appropriate for the gestational age, and the fluid volume around the fetus was normal. At 22.5 weeks gestation, we found the collapsed amniotic membranes attached to the placental insertion of the umbilical cord in the posterior uterine wall (Figures 14 and 15). A spectral Doppler study of the umbilical artery showed normal impedance indices (pulsatility index, Figure 3. Transvaginal sonogram at 13 weeks. The longitudinal scanning plane is at the level of the fetal head and upper and lower limbs. The amniotic membrane (arrow) loosely wraps the fetus. Amniotic fluid volume is diminished, and chorionic space (asterisk) is expanded. 1746 J Ultrasound Med 2005; 24:1745 1751
Leibovitz et al Figure 4. Transvaginal sonogram at 13 weeks. The axial plane is at the level of the fetal abdomen. The amniotic membrane (arrow) loosely wraps the fetus. Amniotic fluid volume is diminished, and chorionic space (asterisk) is expanded. Figure 6. Transvaginal sonogram at 13 weeks. Longitudinal view of the lower left limb shows typical clubfoot deformity. 1.15; and resistive index, 0.69). The fetal growth was in exact correlation to the week of gestation. There was no evidence of amniotic band formation around the fetal limbs. The intrauterine fluid volume was normal. After detailed discussions with the patient regarding the risk of a potential cord impairment 4,5 and the associated consequences, it was decided to continue the pregnancy. A weekly biophysical profile assessment and a spectral Doppler examination of the umbilical cord were performed with nonstress tests after 24 weeks gestation. The consecutive follow-up was uneventful concerning the fetal growth and biophysical parameters. The sonographic examinations performed throughout the rest of the pregnancy Figure 5. Transvaginal sonogram at 13 weeks. The axial plane is at the level of the fetal head. The amniotic membrane (arrow) loosely wraps the fetus. Amniotic fluid volume is diminished, and chorionic space (asterisk) is expanded. revealed normal spectral Doppler measurements in the umbilical artery, with a persistent finding of membranes anchored to cord at the placental insertion but without signs of amniotic banding around the fetal extremities. At 35 weeks gestation, the membranes ruptured. Because of the previous cesarean delivery and the patient s request, a cesarean delivery was performed. A healthy neonate weighing 2450 g, with Apgar scores of 10 at both 1 and 5 minutes, was delivered. No structural abnormalities were found except for the left clubfoot. The placenta had a normal appearance. The amniotic sac appeared as an 8 5-cm collapsed cavity attached to the umbilical cord insertion site. Adjacent to this site was a 3.5 1.5-cm orifice in the amniotic sac (Figures 16 and 17). Figure 7. Transvaginal sonogram at 15 weeks. The axial plane is at the level of the fetal head. The amniotic membrane (arrows) is separated from the chorion. Amniotic fluid volume is near normal. The asterisk signifies the chorionic cavity. J Ultrasound Med 2005; 24:1745 1751 1747
Fetal Escape From the Amniotic Sac Figure 8. Transvaginal sonogram at 15 weeks. The axial plane is at the level of the fetal abdomen. The asterisk signifies the chorionic cavity. The amniotic membrane (arrows) is separated from the chorion. Notice the intra-amniotic location of the fetus. Histologic slides of the attached sac confirmed its amniotic nature (Figure 18); however, histologic examination of the fetal placental surface showed a normal chorionic plate lacking amniotic lining (Figure 19). Two years of postnatal follow-up revealed no abnormality except for the unilateral clubfoot, which was corrected successfully. Discussion Two mechanisms of fetal escape were possible in our case. First, all early sonographic examinations (at 11, 13, and 15 weeks) suggested the existence of amniotic fluid leakage into the chorionic cavity. In those examinations, we suspect that the reduced amniotic fluid volume within the floppy amniotic sac was due to the shift of the amniotic Figure 9. Transvaginal sonogram at 15 weeks shows left clubfoot deformity. fluid into the chorionic cavity through the congenital defect in the amnion. It resulted in a subsequent distension of the chorionic space, which would explain the normal dimensions of the whole gestational sac (Figures 2, 4, and 8). Later, the strengthening fetus could escape from the amniotic sac through the preexisting lesion in the amnion by expanding the membranal defect (Figure 16). Second, it is difficult to dismiss the role of amniocentesis in the disruption of the amniotic membrane. In 2003, we reported in this journal a case of amniocentesis complicated by complete CAS followed by total amnion disruption and the appearance of the fetus in the chorionic cavity. 1 In contrast, the case reported here shows a local amniotic defect, which was posteriorly adjacent to the placental insertion of the umbilical cord (Figure 14). The manner by which an anterior uterine wall puncture could leave the anterior amniotic area undamaged but injure the amnion in the opposite wall is unclear. Nevertheless, this possibility should be considered, as well as the combination of the proposed mechanisms. The consequences of prolonged fetal development within the chorionic cavity are unknown. We could find no data in the literature regarding the potential teratogenic effect on the human fetus growing within the intact chorionic space but outside the functioning amniotic sac. According to our sonographic follow-up, the escape occurred between 17 and 20 weeks gestation. The rupture size of the amnion did not exceed 3.5 cm, and the amniotic sac was less than 8 cm in diameter (Figure 16). We hypothe- Figure 10. Transvaginal sonogram at 19.5 weeks: oblique plane of the fetal body. The fetus appears outside the amniotic membranes within the chorionic cavity (asterisk). Free amniotic membranes (arrow) are shown near the fetal body. 1748 J Ultrasound Med 2005; 24:1745 1751
Leibovitz et al Figure 11. Transvaginal sonogram at 19.5 weeks. The oblique plane is at the level of the fetal lower abdomen. The amniotic sheets (arrow) are located in front of the fetal abdomen. Note the umbilical cord color Doppler signals at the abdominal cord insertion. The asterisk signifies the chorionic cavity. Figure 13. Transvaginal sonogram at 19.5 weeks. The fetus appears outside the amniotic membranes within the chorionic cavity (asterisk). Free amniotic membranes (arrow) are shown near the fetal head. sized that, without a developing fetus inside, the amnion stops growing. Interestingly, there were no histologic signs of the re-epithelization of the placental chorionic plate (Figure 19). We observed a distended chorionic cavity during a sonographic examination at 15 weeks gestation. If the fetus would remain within the leaking amniotic sac, we could probably expect a pathologic CAS beyond this week of gestation. Such a finding has been associated with preterm delivery, fetal death, and structural and chromosomal abnormalities. 6 8 The exact mechanism underlying persistent CAS is yet unknown. Our case raises the possibility that an amniotic membrane leak might be a pathologic mechanism that can impair the normal fusion of the chorionic and amniotic membranes. Figure 12. Transvaginal sonogram at 19.5 weeks. The fetus appears outside the amniotic membranes within the chorionic cavity (asterisk). Free amniotic membranes (arrow) are shown near the fetal head. Sonographically, the details of our case resemble the features of the complete postinterventional CAS associated with amniotic membrane disruption. Such forms of CAS may jeopardize the progression of pregnancy. There are several reports of poor outcome in which the umbilical circulation was impaired as a result of an amniotic band around the cord 1 3 ; however, despite the sonographic findings at the placental insertion of the umbilical cord (Figure 15), our case had an uneventful follow-up. We did not observe abnormalities in umbilical artery spectral Doppler studies, and all nonstress tests were reassuring. Figure 14. Transvaginal sonogram at 22.5 weeks shows the placental insertion of the umbilical cord (large arrow). The elongated saccular structure (small arrows) represents the collapsed amniotic sac attached to the umbilical cord at the placental insertion. The fetal head appears outside the amniotic membranes. Notice the posterior location of the placenta. J Ultrasound Med 2005; 24:1745 1751 1749
Fetal Escape From the Amniotic Sac Management of such cases is problematic because there are no established guidelines to follow; however, parents informed consent, hospitalization for close monitoring, serial sonography, and delivery at the earliest signs of fetal distress seem to constitute an appropriate approach. More information about this potentially dangerous complication is needed to define evidence-based management. Figure 17. Macroscopic image of the placenta, amnion, and umbilical cord. The amniotic sac (a.s.) was filled with water through the rupture site (arrow). Figure 15. Transvaginal sonogram at 22.5 weeks with color Doppler image of the details from Figure 14. The placental insertion of the umbilical cord is signified by the large arrow. Small arrows indicate the collapsed amniotic sac attached to the umbilical cord at the placental insertion. The fetal head appears outside the amniotic membranes. See Figure 16 for correlation. Figure 18. Histologic image of the amnion. This view shows a normal epithelial lining in the inner wall of the sac. No chorionic tissue is in its outer wall. Figure 16. Macroscopic image of placenta, amnion, and umbilical cord. A small, collapsed amniotic sac (a.s.) is attached to the placental insertion of the umbilical cord (white arrow). See Figures 14 and 15 for correlation. Note the edges of the amnion rupture (black arrows) adjacent to the cord insertion. Figure 19. Histologic image of the amnion. The chorionic plate of the fetal surface of the placenta does not show the amniotic layer; thus it directly faces the intrauterine environment (arrow). C.V. indicates chorionic villi within the intervillous space. 1750 J Ultrasound Med 2005; 24:1745 1751
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